The present invention relates to an electrostatic spraying apparatus having electrode plates for repelling the charged particles of sprayed paint. More particularly, the invention relates to an improved rotary electrostatic spraying apparatus suitable for depositing paint on a broad travelling web.
Electrostatic spraying uses the principle of electrophoresis that electrically polarized particles are attracted to a grounded or oppositely charged surface. The conventional electrostatic spraying equipment consists of a spray booth and a disc, bell or gun type applicator that sprays the charged particles of paint onto articles suspended from hangers being transported on a conveyor rail. A metered amount of paint is supplied to the rapidly rotating disc, bell or gun; centrifugal force spreads the paint to the periphery of the disc or bell, or the needle tip of the gun, which is charged to a high negative potential, and on reaching the edge of the disc or bell, or the needle tip, the paint is atomized as a result of the influence of the concentrated electrostatic field at that point, and, as the article to be coated is grounded, the finely divided charged particles are attracted to its surface.
The present invention relates to an effort to modify the above-described rotary electrostatic spraying apparatus so as to apply a uniform coating in the transverse direction onto a broad travelling metal web.
The paint particles sprayed from the conventional rotary electrostatic coating machine provide a characteristic circular or annular pattern. The size of this spray pattern can be controlled by changing the distance between the rotating electrode and the article to be coated, but the paint deposition is not uniform in the direction of the width of a broad travelling web. This problem could be eliminated by reciprocating the coating machine in many directions, but this requires an elaborate coating system and increases the spray cost and maintenance.